[feature] Add boehm gc finalizer (#11446)

lib/system/mmdisp.nim

@@ -99,6 +99,8 @@ when defined(boehmgc):
     ## Return the total number of bytes allocated in this process.
     ## Never decreases.
 
+  proc boehmRegisterFinalizer(obj, ff, cd, off, ocd: pointer) {.importc: "GC_register_finalizer", boehmGC.}
+
   proc allocAtomic(size: int): pointer =
     result = boehmAllocAtomic(size)
     zeroMem(result, size)
@@ -155,9 +157,14 @@ when defined(boehmgc):
     when hasThreadSupport:
       boehmGC_allow_register_threads()
 
+  proc boehmgc_finalizer(obj: pointer, typedFinalizer: (proc(x: pointer) {.cdecl.})) =
+    typedFinalizer(obj)
+
   proc newObj(typ: PNimType, size: int): pointer {.compilerproc.} =
     if ntfNoRefs in typ.flags: result = allocAtomic(size)
     else: result = alloc(size)
+    if typ.finalizer != nil:
+      boehmRegisterFinalizer(result, boehmgc_finalizer, typ.finalizer, nil, nil)
   proc newSeq(typ: PNimType, len: int): pointer {.compilerproc.} =
     result = newObj(typ, addInt(mulInt(len, typ.base.size), GenericSeqSize))
     cast[PGenericSeq](result).len = len